1. Field of the invention
This invention relates to a plane antenna for a GPS (global positioning system), and more particularly to an improvement of a resin casing which accommodates a plane antenna element.
2. Related art
As is well known in the art, a GPS plane antenna is designed as follows: That is, in order to receive radio waves from a GPS artificial satellite, the plane antenna is magnetically mounted, for instance, on the metal roof panel of an automobile. The conventional plane antenna is designed as shown, for instance, in FIG. 3
In the conventional plane antenna, as shown in FIG. 3, its antenna body 1A is made up of an antenna element 1a, and a circuit board 1b on which its relevant circuit elements are mounted. The antenna body 1A is accommodated in a water-proof and dust-proof resin casing, which is fixedly mounted on a roof panel X or the like. The resin casing is formed by injection-molding. The resin casing thus formed has a bottom cover 3A, on the outer (lower) surface of which a fixing permanent magnet 2A is fixedly mounted. After the antenna body 1A has been mounted on the inner surface of the bottom cover 3A, the bottom cover 3A (the inner surface side) is covered with a top cover 4A.
The antenna body 1A set in the resin casing be affected by its ambient electric or magnetic field. Hence, In order to prevent the antenna body 1A from being adversely affected by the ambient electric or magnetic field on the side of the roof panel X, a conductive aluminum-vapor-deposited sheet 5A, which may be used as a name plate when necessary, is bonded to the bottom of outer surface of the bottom cover 3A.
In this case, the aluminum-vapor-deposited sheet 5A, which may be the name plate as the case may be, is employed as was described above. Of course, it is necessary to specially form the aluminum-vapor-deposited sheet 5A. The sheet 5A is relatively high in manufacturing cost. In addition, since it is necessary to bond the sheet 5A to the bottom cover, the number of manufacturing steps is increased as much.